Measures of fish community size structure as indicators for stream monitoring programs

Abstract

Characterization of community size structure presents an alternative to taxa-based approaches commonly applied to assess lotic ecosystem health. However, few studies have explored the relationship between community size structure and land use stresses in lotic systems. In the present study, we investigated use of metrics including mean body size, body size range, size diversity, size evenness, and the size spectrum slope as indicators of land use disturbance in streams. We also explored the effects of sampling intensity (one- versus three-pass electrofishing) on these size-based variables. We found significant decreases in size range and diversity with increased urban cover. In contrast, mean body size, size evenness, and size spectrum slopes were unrelated to variation in land use. Fewer than 25% of samples collected conformed to the power law model predicted for size distributions in aquatic ecosystems. However, increased departure from the power law form was related to agricultural cover and the use of three-pass electrofishing.